Merge pull request #526 from dotty-staging/fix/#522

Fix #522.

Author: odersky

src/dotty/tools/dotc/transform/FullParameterization.scala

@@ -116,8 +116,9 @@ trait FullParameterization {
     info match {
       case info @ PolyType(mtnames) =>
         PolyType(mtnames ++ ctnames)(
-          pt => (info.paramBounds ++ mappedClassBounds(pt))
-            .mapConserve(_.subst(info, pt).bounds),
+          pt =>
+            (info.paramBounds.map(mapClassParams(_, pt).bounds) ++
+             mappedClassBounds(pt)).mapConserve(_.subst(info, pt).bounds),
           pt => resultType(mapClassParams(_, pt)).subst(info, pt))
       case _ =>
         if (ctparams.isEmpty) resultType(identity)

tests/pos/extmethods.scala

@@ -5,3 +5,8 @@ class T[A, This <: That1[A]](val x: Int) extends AnyVal {
   final def loop(x: This, cnt: Int): Int = loop(x, cnt + 1)
   def const[B](): Boolean = return true
 }
+
+class Foo[+A <: AnyRef](val xs: List[A]) extends AnyVal {
+  def baz[B >: A](x: B): List[B] = ???
+}
+